Self-assembly has emerged as a powerful fabrication technology for fabricating macroelectronic devices. Macrofabrication technologies typically integrate a large number of various functional components over areas exceeding the size of a typical semiconductor wafer and do so in a cost-effective and time-efficient fashion. A typical self-assembly macrofabrication technique includes functional devices that are batch microfabricated (for example, on a semiconductor substrate) and released to yield a collection of free-standing components. These components are then allowed to self-assemble onto a template, for example, on a plastic substrate, to yield a functional macroelectronic system. Because self-assembly is an inherently parallel construction method, it allows for cost-effective and time-efficient integration of a large number of functional components onto both conventional (e.g., semiconductor) and unconventional (e.g., plastic) substrates.
An additional benefit of self-assembled macrofabrication is that it allows for the integration of components made from incompatible microfabrication processes (e.g., light-emitting diodes made in compound semiconductor substrates and silicon transistors) onto nonplanar and/or flexible substrates.
The components of a self-assembly based macroelectronic fabrication system typically include: (1) the development of fabrication processes that generate free-standing functional components; (2) the implementation of recognition/binding capabilities to guide the components to bind in the correct location; and (3) the determination of self-assembly procedures/conditions that result in a final assembled system with a high yield of components in correct locations. An exemplary fluidic self-assembly method is disclosed in International Patent Application No. PCT/US2007/072038, filed Jun. 25, 2007, which is hereby incorporated by reference in its entirety. Additionally, fluidic self-assembly has been used to fabricate macro-scale electronics comprising an integrated optical analysis system in International Application No. PCT/US2008/050104, which is also hereby incorporated by reference in its entirety.
Briefly, the above-referenced international patent applications describe a method for self-assembly that accomplishes the assembly process in one step, obviating or mitigating the need for post-processing of an assembled macro-electronic device. Microcomponents are fabricated having a particular shape, and a template with embedded interconnects is fabricated having recessed binding sites that are sized to receive particular microcomponent types. The binding sites include a low melting point alloy for electrically connecting received microcomponents to the interconnect network. The template is placed in a liquid, and the microcomponents are introduced to the liquid such that the microcomponents flow or slide along the template propelled by gravity and/or fluid-dynamic forces and some of them are received into the binding sites, and retained by capillary forces. The liquid is heated before or after introduction of the microcomponents to melt the alloy. The fluid and/or template are then cooled to harden the alloy, binding the microcomponents.
Prior macro-scale self-assembly techniques have produced macroelectronic devices having structures such as light-emitting diodes, photosensors, and transistors, to name a few. One aspect of previous macroelectronic self-assembled devices is the limitation of fabrication to patterning features on one side of a device. In a typical fabrication procedure for components for macro-scale self-assembly, micron-scale devices are patterned on a substrate and then released for self-assembly.
Given traditional microelectronic fabrication techniques, it is not surprising that only one side of the micron scale devices can be patterned, because only the top side of a substrate is typically processed in microfabrication. This remains true when fabricating micron-scale devices for macroelectronic self-assembly, in that only the top side of a device is typically patterned and processed to create the device structure. The eventual bottom side of the device is buried within (or adjacent to) the carrier substrate during processing, and the bottom of the device is only revealed once the devices are released from the carrier substrate, at which point the devices are individually articulated and batch processing of a plurality of such devices would be nearly impossible.
A processing technique enabling the patterning of both the top and bottom sides of micron-scale devices for fluidic self-assembly of macroelectronics would enable more complex devices (both on the micro and macro-scale) and increase the number of currently available types of device structures. By allowing more complex features to be integrated onto macroelectronic devices, the functions of such devices will potentially be improved, expanded, and enhanced.